Problem: $w_1=9[\cos(10^\circ)+i\sin(10^\circ)]$ $w_2=7[\cos(21^\circ)+i\sin(21^\circ)]$ Express the product of $w_1$ and $w_2$ in polar form. Angle measure should be in degrees. No need to use the degree symbol. $w_1\cdot w_2= $
Background For any two complex numbers $z_1$ and $z_2$ (whose radii are $r_1$ and $r_2$ and angles are $\theta_1$ and $\theta_2$ ): The radius of $z_1\cdot z_2$ is the product of the original radii, $r_1 \cdot r_2$. The angle of $z_1\cdot z_2$ is the sum of the original angles, $\theta_1 + \theta_2$. In other words, suppose the polar forms of $z_1$ and $z_2$ are as follows, $z_1 = r_1[\cos(\theta_1) + {i}\sin(\theta_1)]$ $z_2 = r_2[\cos(\theta_2) + {i}\sin(\theta_2)]$, then the polar form of their product is: $z_1z_2 = r_1r_2[\cos(\theta_1 + \theta_2) + {i}\sin(\theta_1 + \theta_2)]$. [How do we get this?] Finding the radius of $w_1\cdot w_2$ $w_1=9[\cos(10^\circ)+i\sin(10^\circ)]$ $w_2=7[\cos(21^\circ)+i\sin(21^\circ)]$ Here, $r_1=9$ and $r_2=7$. Therefore, the radius of $w_1\cdot w_2$ is $r_1\cdot r_2=9\cdot7=63$. Finding the angle of $w_1\cdot w_2$ $w_1=9[\cos(10^\circ)+i\sin(10^\circ)]$ $w_2=7[\cos(21^\circ)+i\sin(21^\circ)]$ Here, $\theta_1=10^\circ$ and $\theta_2=21^\circ$. Therefore, the angle of $w_1\cdot w_2$ is $\theta_1+\theta_2=10^\circ+21^\circ=31^\circ$. Summary We found that the radius of $w_1\cdot w_2$ is $63$ and its angle is $31^\circ$. Therefore, $w_1\cdot w_2=63\left(\cos(31^\circ)+i\sin(31^\circ)\right)$